bass port

Front

which is best, bassport in rear of cabinet or front

As [fb] is approached, output from the port increases while that of the driver approaches a null. Therefore, front ports are preferred. When [fb] is very low, then a rear port may be used instead. Here, signal wavelength is many times longer than the distance between the driver and the port, and port noises due to increased air-flow are obscured.

Regards,
WHG
 
Port size

I know there must be a formula somewhere, but I am new to this forum. I know AB from the Altec users forum. I thought this might be a better place to post this question.

I am building speaker enclosures and need to determine port size. Using speaker specs anlog with enclosure dims, there is a formula for determing port size. Could someone please point me in the right direction.
Thanks,
MM
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
I know there must be a formula somewhere, but I am new to this forum. I know AB from the Altec users forum. I thought this might be a better place to post this question.

I am building speaker enclosures and need to determine port size. Using speaker specs anlog with enclosure dims, there is a formula for determing port size. Could someone please point me in the right direction.
Thanks,
MM

Lv=2360*Dv^2/(Fb^2*Vb)-0.73*Dv
Lv, Dv in mm, Vb in liters
 
Presuming the port is tuned low, it shouldn't make much acoustic difference where it is placed. Rear ports can be harder to position (needs to be several radii away from the wall or other obstacles). But since some midrange can reflect/leak out through the port, and the port may have its own resonant peak, front placement may aim that right at the listener.

My "Safe" rule of thumb for port size was 3" for an 8"; 4" for a 10"; 5" for a 12." Smaller than that, best check a simulation to see that at maximum output the flow is still a low % of the speed of sound. Yes, it can become hard to fit the port. NO you should not bend it, I don't care what anyone says. End flares/flanges help at medium SPLs but actually not at high SPL, according to JBL research.